Strand-shaped material in the context of the present invention (hereinafter also referred to as winding material) comprises wire-, braid-, filament-, rope-, or fiber-type materials, in particular of electrically conductive material, having a uniform cross-section throughout its length and the characteristic of being flexible and absorbing plastic and/or elastic deformations. Generally, this winding material is provided with an electrically insulating sheath. Appropriate materials can be formed into coils around the carrier body, turn by turn, by a relative movement between the carrier body and the strand-shaped material feeding device.
An example for the strand-shaped material is enameled copper wire which may be provided as a round wire or a flat wire. Carrier bodies with non-circular cross-sections are, for example, the pole teeth of laminated sheet metal packages of electric motors. For functional performance of the electric motor, energizable coils have be to applied thereto. However, between two adjacent pole teeth which radially extend inwards or outwards from a circular ring that is referred to as a yoke, there is only limited usable space available which often provides only limited accessibility. This space should be utilized to an optimum.
There are limits to such a maximum utilization of the winding space for current-carrying conductor cross-sections (maximization of the filling factor). These limits result on the one hand from the geometry of the strand-shaped winding material due to which so-called gore spaces between round wires cannot be avoided. On the other hand, limits are imposed by the employed winding method when a wire fails to be placed in contour-conforming manner along the surface line of a carrier body, such as for example a pole tooth.
‘Contour-conforming’ is to be understood as a continuous tangential engagement of the winding material to the surface of the carrier body to be wound with respect to the circumferential length of a turn between two corner points of the cross-section that act as bending points, all this considered for the first layer of a coil. For all further layers of a so started coil, ‘contour-conforming’ means a continuous tangential engagement of the winding material to the contour-conformingly laid turns of the preceding layer.
Contour-conforming laying is influenced, and in particular impeded, by material properties of the winding material, because the material opposes a change of shape induced by the bending operation during winding by plastic or elastic reactions. While a circular cross-section of the carrier body results in a continuous, constant bending stress of the winding material for which the tension force to be applied can be optimized, a rectangular cross-section, e.g., having a length/width ratio>>1 as is typical for tooth poles, results in an abruptly increasing bending stress at the deflection points of the four corners, followed by laying up the wire on the adjoining side of the carrier body with hardly any load. This permits the wire to spring back which then causes that the turn forms a bulge relative to the carrier body. The resulting space between the turn and the carrier body is lost for laying up useful conductor cross-sections.
If instead of a round enameled copper wire a flat wire is used, for example, the conditions for the transfer of a wire from a wire nozzle or guidance roller to the carrier body is further complicated. The term ‘bulge’, also referred to as ‘bulging’ describes a laid-up state of the winding material on the carrier body wherein one turn or all turns laid in the same section between two bending deflection edges fail to be laid with contour-conforming engagement. The bulge or bulging is the space between the surface of the carrier body and the most proximate turn, measured in the middle of the distance between two adjacent bending deflection edges. The extent of bulging depends on the wire diameter, the applied tension force and the distance between the bending deflection points.
Another hindrance for a contour-conforming lay-up of the winding material is the accessibility of the carrier body for the winding material laying device, which accessibility is given by the geometry of the product. This is especially of concern if the carrier bodies are provided as a multi-tooth pole assembly, to remain with the example of tooth poles. The accessibility of the winding space limits the degrees of freedom available for adjusting the winding material supplying device to an optimum, in terms of distance, direction, and guiding action with respect to the lay-up point on the surface of the carrier body. The winding material supplying device has to be adapted to the conditions of accessibility. Tubular nozzles, for example, have proved suitable for this purpose, which nozzles can operate in the winding space and perform a translational relative movement with respect to the carrier body, while the carrier body itself realizes a complementary pivoting movement.
There are prior art solutions to achieve a closely packed arrangement of the strand-shaped winding material, in particular winding wire, and a maximum possible utilization of the theoretically available winding space between opposing flanks of two support bodies, such as tooth poles of stators for electric motors. An additional condition resulting therefrom is that the thereby approaching sides of the coils in such a winding space adapt to form almost parallel flanks, however with a corrugation of their circumferential contour which may, for example, correspond to half the diameter of a round winding wire. A bulging which may arise during the winding of the coil at the longitudinal sides thereof is detrimental to this objective.
Among the proposals for solution, orthocyclic laying of the winding layers of such a coil holds a special place, because of the high fill factor obtainable. Orthocyclic winding means that the turns of a round wire coil are not formed in helically progressing manner on the circumferential surface of the carrier body; namely, in case of helical formation larger gore spaces result at the flanks of limiting flanges, and moreover the opposite handedness of successive layers ultimately results in a pell-mell of individual turns which interrupts the desired side-by-side winding of the turns and results in a so-called wild layer structure with packing density losses. Instead, in orthocyclic winding the turns are laid at an angle of 0° to the axis of rotation of, e.g., a cylindrical carrier body, and before completion of a full turn the wire is deflected by the amount of its diameter, within a short circumferential length.
DE 10 2007 037 611 B3 proposes to place the point of discontinuity in the turns of an orthocyclic coil at a narrow end face of the pole tooth, because it is there where it causes the least disturb of the relative flatness of the opposing longitudinal surfaces of adjacent pole coils. In order to reliably obtain the jump in the turns at the narrow side and to achieve a reliable transition to the adjoining longitudinal side, the carrier body is provided with a special contour. This comprises to form one of the two longitudinal sides of the contour with a prolonged length, whereby a larger laying length results at the corresponding, now inclined end face which can be used to realize the jump. In addition, a beneficial fixing effect is obtained at the sharp corner of about 60° for the wire deflected there. A disadvantage is the acceptance of an axial prolongation of the carrier body beyond the minimum size functionally required for the stator of the motor.
An object in DE 10 2007 002 276 A1, equally, is to use the existing winding space of a pole tooth coil as efficiently as possible and therefore to avoid individual turns or overcrossing turns to project from the longitudinal sides of the coils, by applying orthocyclic winding, modified for the case of an odd number of layers and the default to place both ends of the coil at the same flange side. To this end, the jump of the turns and the winding layer jump is spread at the longitudinal sides. Thus, an embedment is provided for the spread windings of the last layer by offsetting the projecting overcrossings to the less critical end faces.
EP 1315268 A1 describes a coil wound around a pole tooth according to the above mentioned winding technique with bulging at the longitudinal sides. To avoid an unwanted bulge, a complex winding unit is proposed by means of which the coils of a strong round wire—such as particularly required for products in the automotive sector due to the on-board wiring low voltages—are pre-wounded separately, which is done under cyclic activation of radially adjustable bending rams and the like. This is only possible because accessibility is enabled by holding the winding tool separated. It is even accepted here, that the placed pole coils cannot be wound in a connected assembly with complete strands.